The maintenance of tropical, sub-tropical, and temperate aquaria requires a delicate balance of macro nutrients including nitrogen (N), phosphorus (P), potassium (K), and carbon (C). Overabundance of nutrients can lead to detrimental pH fluctuations, overgrowth of nuisance organisms, and reduced health and/or growth of organisms in the aquarium. For example phosphate inhibits coral's ability to deposit new skeletal growth. The devices and methods of the present invention function to provide a balance of nutrients in an aquarium or aquaculture system.
The devices of the present invention differ from refugiums in several key ways. Refugiums are external tanks that are connected to the main aquarium tank and serve as a separate location for the growth of plants and/or animals free from predation by, e.g., fish in the main tank. Refugiums can be used to support the growth of macroalgae in attempt to control nutrient levels in the main tank. Refugiums, however, are not considered to be an efficient means of controlling nutrient levels or diurnal pH swings. Due to inefficient water flow and lighting, refugiums are not sufficient to control excess nutrients like phosphate and/or prevent daily swings in pH. Further, refugiums are open to the atmosphere allowing direct incorporation of carbon from the air, which can lead to the synthesis of dissolved organic carbon compounds (e.g., polysaccharides) that yellow the water.
Walter H. Adey (U.S. Pat. Nos. 4,966,096 and 5,097,795) describes a “water purification system” that contains a screen that provides an algal-growing surface placed in a moveable, substantially flat, horizontally-positioned, tray-shaped receptacle. The apparatus described by Adey utilizes microalgae in an open-air system that incorporates mechanisms for exposing the algal turf to simulated tide and waves. These devices incorporate complicated mechanisms to simulate surf. For example, in an embodiment described by Adey, the tray, on which the algal turf attaches, accumulates water from the aquarium tank until the weight of the water causes the tray to tilt, dumping the water and allowing the tray to return to its original horizontal position.
Kyle R. Jensen (U.S. Pat. Nos. 5,527,456; 5,573,669 and 5,846,423) describes a method for purifying water that comprises a flat waterway with a screen or similar substrate at the bottom as a microalgae growing surface. Jensen, like Adey utilizes an open-air system with periodic surges of water over the surface of the algal turf.
The present invention offers several advantages over the prior art. The present invention provides an optimal exposure to light to facilitate growth of the macroalgae, which is utilized as part of the invention. The present invention also provides ease of maintenance and the ability to control the levels of one or more nutrients in the main tank via bioadsorption by the macroalgae and nutrient supplementation. In one embodiment, the bioreactor of the present invention provides a closed loop system that is not directly exposed to the atmosphere, limiting the contained macroalgae to carbon from the main tank. In addition, the present invention avoids the complicated mechanisms described by Jensen and Adey.